The present invention pertains to a blind nut. More particularly, it pertains to a blind nut on which the outer circumferential shape of the internal threaded portion is optimized with consideration for the distribution of tension placed on the internal threaded portion of the nut.
A blind nut comprises an internal threaded portion, a tubular portion continuing from the internal threaded portion, and a flange at the end portion of the tubular portion. Using a fastening device such as the one set forth in Japanese Published Unexamined Patent Application 2004-188558, the blind nut is inserted through a hole in an attached-to member with the screw mandrel of the fastening device threaded into the internal threaded portion; the screw mandrel is retracted, buckling the tubular portion so as to expand its diameter; and the attached-to member is sandwiched between the buckled tubular portion and the flange, affixing the blind nut to the attached-to member. The male thread of a bolt can be engaged with the internal threaded portion of this blind nut to attach an attaching member to an attached-to portion. The blind nut permits work to be performed from one side of the attached-to member, thereby facilitating the fastening of nuts to members which cannot be worked on from the reverse side, such as panels or other attached-to members.
FIG. 1 is a front elevation showing a conventional blind nut 10 viewed in cross section. Blind nut 10 has a cylindrical form which is entirely axially symmetrical about its center axis, having an internal threaded portion 11 at one end. Internal threaded portion 11 is cylindrical, and has formed within it an internal thread 15. The external thread of a fastening device can be caused to engage internal thread 15. The tubular portion 13 continuing on internal threaded portion 11 is cylindrical; it has a thinner wall than internal threaded portion 11 and is the part that buckles when attaching to attached-to member 41. Blind nut 10 has a flange 14 at the end opposite internal threaded portion 11. The outside diameter of flange 14 is greater than the inside diameter of attaching hole 43 in attached-to member 41, and when blind nut 10 is inserted in the attaching hole 43 in attached-to member 41, the bottom surface of tubular portion 13 contacts the top surface of attached-to member 41 and stops. A through hole 16 is formed from the flange 14-side end portion to the internal threaded portion 11-side end portion. The inside diameter of through hole 16 from the flange 14-side end portion to the internal threaded portion 11-side end portion is constant, and the inside diameter diminishes in internal threaded portion 11.
FIG. 2 is a front elevation showing a partial section after blind nut 10 has been attached to the attaching hole 43 in attached-to member 41. When blind nut 10 is attached using a fastening device, thin-walled tubular portion 13 buckles so as to expand in diameter, becoming expanded diameter portion 17; attached-to member 41 is sandwiched between expanded diameter portion 17 and flange 14, and blind nut 10 is attached to attached-to member 41.
Generally, when tubular portion 13 is caused to buckle and a blind nut 10 is attached, a strong tensile force is placed on internal threaded portion 11; internal threaded portion 11 therefore requires sufficient strength to prevent deformation. Conventionally, however, no consideration was given to the distribution of tensile force placed on the internal threaded portion 11 of blind nut 10 when determining the wall thickness of internal threaded portion 11. Therefore, a risk existed that internal threaded portion 11 would deform when attaching a blind nut. If the wall thickness was greater than necessary, excessive amounts of material may have been used, increasing weight and driving up cost.
JP Published Unexamined Patent Application 2010-42503 discloses a method for manufacturing a threaded blind nut (blind nut) from metal. This method includes a cold forming stage for partially forming the insert, except for the internal thread, using a cold forming method, a screw cutting stage for cutting the internal thread, and a stage for tempering of appropriate parts of the insert in order to promote post-deformation during installation.
On the blind nut of JP Published Unexamined Patent Application 2010-42503, a tapered portion is disposed between the internal threaded portion and the tubular portion; a tapered portion is also disposed on the tip portion of the internal threaded portion, and the internal threaded portion diameter gradually decreases toward the tip.
However in the blind nut of JP Published Unexamined Patent Application 2010-42503, the determination of the wall thickness of the internal threaded portion does not go so far as to consider the distribution tensile force amounts placed on the internal threaded portion. Hence, there is a risk that the internal threaded portion will deform and break due to tensile force placed on the internal threaded portion when the blind nut is attached. Or, the wall thickness of the internal threaded portion may be increased unnecessarily, producing a heavy and costly blind nut.
U.S. Pat. No. 3,948,142 discloses an integral blind nut comprising a body member having an end part with an internal thread. On the end portion opposite the end portion (internal threaded portion) having the internal thread, a sawtooth-shaped end part is provided in order to attach the blind nut to a work piece without rotating. A deformable wall portion (tubular portion) is provided between the end portion with internal thread and the sawtooth-shaped end portion.
The internal threaded portion of the blind nut in U.S. Pat. No. 3,948,142 has a narrow-tipped part, a thick part adjacent to the deformable wall portion (the tubular portion), and a tapered portion between them. However, the blind nut of U.S. Pat. No. 3,948,142, similar to the blind nut of JP Published Unexamined Patent Application 2010-42503, does not consider the distribution of tensile force amounts placed on the internal threaded portion. Hence, there is a risk that when the blind nut is attached, the internal threaded portion will be stretched out, expanding radially and breaking the blind nut. Or, the wall thickness of the internal threaded portion may be increased unnecessarily, producing a heavy and costly blind nut.
JP Published Unexamined Patent Application 2004-11876 discloses a blind nut comprising a main member made up of plastically deformable metal or the like, and a nut member made of a rigid material such as metal or the like, separate from the main member. The main member has a hollow tubular portion and a flange at one end thereof. The nut member has an internal threaded portion and a linking portion. The main member receives the nut member on the inside. The extended portion of the tubular portion of the main member is linked to the linking portion of the nut member.
In the first embodiment of JP Published Unexamined Patent Application 2004-11876, a knurled channel is formed extending in the longitudinal direction on the outside surface of the blind nut main member. In another embodiment, a projection biting into the attached-to member is formed on the bottom surface of the flange. This prevents the blind nut from slipping relative to the attached-to member when a bolt is engaged in the nut member and tightened.
However, in the nut member of the blind nut in Patent Reference 3, the wall thickness of the internal threaded portion is uniform, and no consideration is given to the fact that the tensile force placed on the internal thread end portion is greatest. Hence, there is a risk that when the blind nut is attached, the internal threaded portion will be stretched out, expanding in the radial direction and breaking the blind nut. Or, the wall thickness of the internal threaded portion may be increased unnecessarily, producing a heavy and costly blind nut. Therefore, a blind nut has been sought with sufficient strength to withstand the tensile force placed on the internal threaded portion when a blind nut is attached.
Further, a light-weight and low-cost blind nut has been sought. In addition, a blind nut has been sought which does not turn easily at the time of and subsequent to attachment to an attached-to member.
One object of the present invention is therefore to provide a blind nut having sufficient strength to withstand the tensile force placed on an internal threaded portion when the blind nut is attached to an attached-to member. Another object of the present invention is to provide a light-weight and low-cost blind nut. Another object of the present invention is to provide a blind nut capable of reliable attachment to an attached-to member without rotating freely.